locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER

The owner field in the rw_semaphore structure is used primarily for
optimistic spinning. However, identifying the rwsem owner can also be
helpful in debugging as well as tracing locking related issues when
analyzing crash dump. The owner field may also store state information
that can be important to the operation of the rwsem.

So the owner field is now made a permanent member of the rw_semaphore
structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 2ea18a3def04..148983e21d47 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -34,12 +34,12 @@
  */
 struct rw_semaphore {
         atomic_long_t count;
-#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
         /*
-         * Write owner. Used as a speculative check to see
-         * if the owner is running on the cpu.
+         * Write owner or one of the read owners. Can be used as a
+         * speculative check to see if the owner is running on the cpu.
          */
         struct task_struct *owner;
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
         struct optimistic_spin_queue osq; /* spinner MCS lock */
 #endif
         raw_spinlock_t wait_lock;
@@ -73,13 +73,14 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
 #endif
 
 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
-#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
+#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED
 #else
 #define __RWSEM_OPT_INIT(lockname)
 #endif
 
 #define __RWSEM_INITIALIZER(name)                               \
         { __RWSEM_INIT_COUNT(name),                             \
+          .owner = NULL,                                        \
           .wait_list = LIST_HEAD_INIT((name).wait_list),        \
           .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
           __RWSEM_OPT_INIT(name)                                \